1. Field of the Invention
The present invention generally relates to communications between electronic circuits and, more specifically, to the transmission of digital data in a master-slave system. The present invention more specifically applies to communications over a so-called open-drain or open-collector bus (according to the MOS or bipolar technology), conveying both data and the power supply of the slave circuit(s).
2. Discussion of the Related Art
In an open-drain (or open-collector) bus, the data conductor of the bus is, in the idle state, at a voltage different from ground (generally, a positive voltage). The data are coded and then transmitted by pulling of the bus to ground according to a pre-established coding enabling the receiver to decode the data.
In a single-wire bus protocol to which the present invention more specifically applies, a single communication wire (in addition to a common reference or ground) is used. The signal transmitted over this bus is used as both a synchronization and a data signal. Further, the signal may also be used to power the slave circuit.
In the idle state, such a bus is pulled by default to the high state with a non-zero impedance and the different circuits (master or slave) pull the bus to zero by means of a transistor connected to a lower level (generally the ground) to code the transmitted data.
An example of a system of communication over a single-wire bus of this type is described in U.S. Pat. No. 7,636,806. According to the communication protocol described in this document, the data coding is performed according to periods of fixed levels separating two state switchings. The bits at state 1 (high) are coded by periods having a longer duration that the bits at state (low), each transition between the high state and the low state indicating a bit change even if the bit state remains the same.
Such a communication protocol operates properly if the slave circuit has its own power supply source. However, in many cases, slave circuits draw their power supply from the bus. The power recovery is then not optimal. Indeed, in average, the bus will only be in the high state capable of providing a power supply to the slave circuits for half of the transmission.